In block transmission systems, typically, a base station transmits a preamble symbol in addition to the data symbols. A preamble symbol is, generally, an introductory symbol that may not carry data but is provided to enable the receiver to perform certain tasks such as synchronization, channel estimation, estimation of base station signal strengths etc. The preamble symbol has a higher density of pilot symbols than the rest of the symbols. The preamble symbol does not contain any data.
Further, the data can be transmitted to a mobile station from either a single base station or from a plurality of base stations. For example, in 802.16e, a base station can transmit data packets that are destined specifically for the mobile station on a unicast zone. On the other hand, data packets that are broadcast/multicast by a plurality of base stations can be received by more than one mobile station on a Multicast and Broadcast Service (MBS) zone.
Wireless channels are characterized by multi-path. The transmitted signal undergoes phenomenon like reflection and scattering from various obstacles. This results in multi-path. Consequently, the mobile station may receive the signals with different delays. Also, signals transmitted by the plurality of base stations may not always take a line-of-sight path in reaching the mobile station. The multi-path nature of the channel in the time domain manifests as a frequency selective channel in the frequency domain.
The combined channel of the plurality of base stations differs from a single channel between a base station and a mobile station. The combined channel has a larger delay spread than the single channel. This results in highly frequency selective channels. The large delay spread hurts the channel estimation of the combined channel.
Some of the existing channel estimation methods employ interpolation techniques such as sinc or Fast Fourier Transform (FFT) based interpolation. In such methods, the delay spread of the channel that can be estimated well is limited.
There is therefore a need for methods and systems for channel estimation such that a delay spread of a channel that can be estimated well is increased and the channel estimation performance is improved.